One Million Cycle Durability Test of Electrochromic Devices Using Charge Balance Control

We fabricated 10 mm × 10 mm WO3 electrochromic devices (ECDs) using a nanoparticle deposition system (NPDS), which is a coating method that uses kinetic spray. NPDS has the advantage of mass production due to its relatively low pressure and low temperature working conditions but can result in porous surfaces, which has a negative effect on device durability. We developed an optical transmittance measurement and voltage control system that allows dynamic control. Transmittance was measured by Optical Power Meter, 2936-R Newport, while voltage was dynamically applied by NI9477, National Instrument. Current was measured by high resolution current, National Instrument. This system enables ECDs to be feedback controlled depending on the measured electronic properties. We then characterized the WO3 ECDs, focusing on the relationship between transmittance and current under well-known static operating conditions. Finally, we proposed a new algorithm to extend durability performance by adopting charge balance control and conducted an accelerated life test over 1,000,000 cycles. According to our results, the optical performance was maintained until the test ended, and there was a 45.4% difference in the maximum and minimum transmittance of the sample after the accelerated life test. Therefore, the charge balance control enhanced the lifetime of the ECDs by avoiding negative charge accumulation, verifying that the durability of ECDs could be enhanced by adopting dynamic control.